You mean the heatsink, which is located directly on top of the CPU?
I'd say you should have the left one blowing air into the case, and the top and back fans blowing out of the case. Never have more fans intaking or you will build up too much air pressure in the case.
I'd say you should have the left one blowing air into the case, and the top and back fans blowing out of the case. Never have more fans intaking or you will build up too much air pressure in the case.